The present invention relates to a method of forming features on a material blank. More particularly, the present invention relates to a method of forming features on a material blank using multiple exposure events.
Photolithography is a technique commonly used for the creation of three dimensional structures on a material blank, such as a substrate wafer, a semiconductor chip, a display device, a detecting device, or image pickup device, for example. The photolithography process generally allows features such as rails, grooves, ridges, tapers or gradients, and other features to be formed on a material blank that begins the photolithography process as one or more substantially flat layers.
Photolithography is often used in the formation of features on a slider for a transducer head apparatus. It may be desired to create tapered comers along the perimeter of the slider, at an air bearing surface (ABS). In addition, it may be desired to create three dimensional formations along an advanced air bearing surface (AABS), such as an AABS located in an interior portion of the slider. Such tapered features are desirable in addressing shock and contact, and also for providing secondary pressurization. Shock includes both operational-shock (i.e., shock occurring while the slider is in use) and non-operational-shock (i.e., shock occurring while the slider is not in use, such as during transportation). Contact is particularly a concern with load-unload disc drive systems, where a slider frequently comes in contact with a medium, such as a textured portion of a disc. Three dimensional features formed on a slider can help mitigate negative effects due to contact between the slider and an adjacent storage medium (e.g., a disc), as well as provide additional air lift force. A slider ABS having patterned, three-dimensional gradient or tapered features has been shown to have better fly capabilities and low-energy contact performance than a convention slider ABS.
In a typical slider fabrication process, individual sliders are initially formed as part of a large wafer that contains numerous individual sliders that are connected together. Photolithography for forming three-dimensional ABS and AABS features on individual sliders is typically conducted at wafer-level manufacturing. At a later point, individual sliders are separated from the wafer.
Generally, photolithography involves the use of a mask placed between an exposure apparatus and a material blank, such as a substrate wafer. The mask includes one or more patterns that are imaged on the material blank by exposing the mask and material blank with the exposure apparatus.
Numerous types of exposure apparatuses are available. For example, 1× steppers are known which produce a pattern on a material blank of the same scale as a pattern on the mask. Also known are reduction steppers that produce patterns on the material blank at a different, generally smaller, scale than the pattern on the mask (e.g., a 4× stepper).
The mask (e.g., a photomask) has at least one mask pattern thereupon. The mask is disposed between the material blank and the exposure apparatus during the exposure process. A typical mask is comprised of chrome and glass, where chrome is applied to the glass to prevent the transmission of light through discrete portions of the mask. Portions of the mask not made opaque by chrome typically allow transmission of some light through the glass to the material blank.
The first step in a photolithography process involves surface preparation, where a surface of the material blank is cleaned and dried. The purpose of cleaning the material blank is to remove any contamination on the surface of the material blank, such as dust, organic, ionic and metallic compounds. The cleaned material blank may be primed to aid adhesion of a photoresist to the surface of the material blank.
Next, a photoresist is applied to the material blank. The photoresist is a thin layer of light-sensitive material that is applied to a surface of the material blank where features will be formed. The photoresist is applied to the material blank at some early stage of the photolithography process, but is typically removed at some later point. A variety of positive and negative photoresist materials are available, and the particular photoresist used is selected according to the particular requirements of a specific application. The photoresist layer is typically applied to the surface of the material blank using a coating apparatus, such as a spin-coating machine, which applies the photoresist in a vacuum.
After the photoresist is applied, a softbake process may be used to promote partial evaporation of photoresist solvents and promote adhesion of the photoresist to the material blank.
Next, after the photoresist is applied and adhered to the material blank (and any softbake processes are conducted), an alignment process is conducted. During alignment, the material blank is precisely aligned relative the mask. The initial alignment is critical, and is conducted in X and Y directions, as well as rotationally. Positioning of the material blank and the exposure apparatus relative the mask will vary according to the type of exposure apparatus used. Types of exposure apparatuses include contact, proximity, and projection exposure machines.
After alignment, an exposure process is conducted where portions of the photoresist layer on the material blank are exposed according to the particular pattern sought to be formed on the material blank. During the exposure process, portions of the photoresist undergo a chemical reaction when illuminated, such as with ultraviolet (UV) light, by the exposure apparatus. Exposure of the mask positioned relative the material blank causes a pattern on the mask to be transmitted to the photoresist layer on the material blank. During the exposure process, portions of the photoresist are typically polymerized according to the desired pattern. In conventional photolithography, a single exposure event transfers all the illumination energy needed to image the desired pattern on the material blank.
In some photolithography systems, a mask includes multiple mask patterns. For example, a single mask may include a rough cut mask pattern and a fine cut mask pattern. During the exposure process, different mask patterns may be used to expose a single exposure site on the material blank (i.e, a discrete region on the material blank within which a distinct pattern is desired to be formed) with different mask patterns, or the same mask pattern may be used to expose different exposure sites on a large material blank. These processes typically involve initiating large-scale lateral movements of the mask, with such large-scale movements typically being of distances greater than a length or width of the mask patterns on the mask.
After the exposure process, a development process is typically conducted, where polymerized photoresist can be hardened and unpolymerized photoresist can be removed, through processes such as a postbake process and the application of a stripping solution.
At this point in the photolithography process, a three dimensional pattern is typically formed on the photoresist layer of the material blank. This transient three-dimensional pattern on the photoresist layer is not necessarily identical to the pattern desired to be finally formed on the material blank. The three-dimensional pattern formed on the photoresist layer is a protective layer of varying depths, with the depth and shape of the three-dimensional pattern on the photoresist varying as a function of the amount of protections desired for particular areas of the material blank.
Next, an etching process is conducted. During the etching process, portions of the material blank itself are removed. The etching process may be conducted using ion milling with charged ions, such as Argon plasma (Ar+), and sometimes along with other chemistry to assist the process. In addition, other techniques known in the art can be utilized. With techniques such as ion milling, the material blank, partially covered by protective photoresist material, is bombarded by ions, which erode or sputter away portions of the material blank. During the etching process, depth and shape of portions of the material blank removed will vary as a function of the three-dimensional pattern formed in the photoresist layer. Typically, areas of the material blank not protected (i.e., not covered) by photoresist material will be etched to a greater depth on the material blank. Accordingly, areas of the material blank protected by greater amounts (i.e, a thicker portion) of the photoresist will be etched to lesser depths of the material blank, if at all. In general, the etching process will depend on the particular materials and factors involved, such as photoresist responsiveness. During the etching process, the material blank may be rotated in order to achieve optimal results, as will be recognized by those skilled in the art.
After the material blank has been sufficiently etched, a final step involves removal of any remaining photoresist material.
In addition, various inspections of the material blank are typically conducted throughout the photolithography process.
Halftone (and grayscale, etc.) masks are a type of mask commonly used with photolithography processes for forming three-dimensional patterns on an air bearing surface (ABS) of a slider. Halftone masks use an array or grid of individual mask units. Individual mask units have a particular transmission intensity level, meaning that a particular percentage of illumination energy is resolved when transmitted through the individual mask units. The array of mask units forms regions with discrete transmission levels. By selecting the location and transmission levels of mask units in the array, a desired mask pattern is created for imaging the particular pattern on a material blank. However, halftone mask photolithography systems, particularly with 1× steppers, often do not permit enough of a gradual change in the transmittance level of the mask to produce smooth or relatively smooth features on the material blank.
High reduction-ratio steppers (e.g., 4× or 5× steppers) can utilize many transmission intensity levels, but such high reduction-ratio steppers are costly. In slider ABS fabrication, 1× steppers are most common due to high throughput and low cost-of-ownership benefits. However, using conventional photolithography techniques, 1× steppers typically do not provide enough transmission intensity levels to form desired features on a slider ABS. More particularly, conventional photolithography using 1× steppers does not produce features having desired smoothness characteristics.
Another type of mask is a high energy beam-sensitive (HEBS) glass mask. HEBS masks allow for gradual changes in the light transmittance properties of the mask, thereby allowing smoother and more detailed features to be formed than with traditional halftone masks. However, HEBS systems are very costly, and are often not compatible with photolithography equipment currently in use in labs and manufacturing facilities for forming ABS features on a slider.
A reflow method can be used to form three-dimensional features. Reflow methods typically involve applying a ductile ball of material to a desired location, and then heating that ball such that the ductile material flows enough to reshape it. However, reflow methods have little design flexibility except for spherical patterns. Thus, reflow methods are not particularly amenable to slider ABS fabrication.
The present invention relates to an alternative method for forming features on a material blank.